Chapter 8Chapter 8Work and Machines

Lesson 1: WorkLesson 1: WorkWork when something moves because of a force being applied

Work = force x distanceLabel is newton-meter or joule

Work formulaWork formula

w

f d

Lesson 2: EnergyLesson 2: EnergyEnergy ability to do workThere are 2 kinds of energy◦Kinetic energy in motion◦KE = ½ mv²◦Potential stored energy◦PE = mghgravity = 9.8 m/s²

6 Forms of Energy6 Forms of EnergyChemical energy stored in the bonds btw. atoms

Heat energy moving particles in matter

Mechanical energy in moving objects

6 Forms of Energy 6 Forms of Energy cont.cont.

Nuclear energy stored in the nucleus of atoms

Radiant energy light energy

Electrical energy causes electrons to move

Energy can be converted from one form to another

Generator device used to convert mechanical energy to electrical energy

Law of conservation of energy energy cannot be created nor destroyed

Lesson 3: LeversLesson 3: LeversSimple machines tool that makes it easier or possible to do work

Lever bar that is free to turn around a fixed point

Fulcrum fixed point around a lever turns

LeversLevers cont. cont.

Effort force (FE force applied to a machine by the user

Resistance force (FR) force applied to the machine by the object to be moved

3 Classes of Levers3 Classes of LeversBased on the position of the resistance, fulcrum, & effort

First-class lever fulcrum is btw effort & resistance

Changes direction of force & can increase force

Examples of class 1 levers include:

Teeter-totter Scissors Pair of pliers

Second-class lever resistance is btw effort and fulcrum

Always increases forceDo not change direction

Examples of class 2 levers include:

Wheelbarrow Crowbar Nut cracker

Third-class levers effort is btw resistance & fulcrum

Increases distance which cause resistance to move further or faster

Examples of class 3 levers include:

Tweezers Stapler

Mousetrap Broom Hockey stick

Efficiency Efficiency A simple machine cannot do more work than the person using it

Machines increase or change the direction of force

If less effort is needed, more distance is needed also

Effort distance & resistance Effort distance & resistance distancedistance

Effort distance (dE) the distance the effort moves

Resistance distance (dR) the distance the resistance moves

Effort distance is greater than resistance distance

Work Input & Work Output Work Input & Work Output Work input work put into a machine by the user◦Work input = FE x dE

Work output work done by a machine against the resistance◦Work output = FR x dR

EfficiencyEfficiencyEfficiency =

work output work input x 100

FR x dR

FE x dE x 100

Lesson 4: Mechanical Lesson 4: Mechanical advantageadvantageMechanical advantage

number of times a machine multiplies its effort force◦Mechanical advantage =

resistance forceeffort force

◦MA = FR

FE

Effort Arm & Resistance ArmEffort arm distance btw the fulcrum & effort force

Resistance arm distance btw the fulcrum & resistance force◦MA = effort arm

resistance arm

Lesson 5: Other simple Lesson 5: Other simple machinesmachines

Pulley wheel w/ a rope, chain, or belt around it

A single pulley changes direction, not force; ma = 1

Fixed pulley attached at topMovable pulley entire pulley & object attached will rise

Pulley Pulley cont.cont.

MA of a pulley = number of ropes that pull upward

The easier to lift an object, the more distance you pull on the rope

Inclined PlaneInclined PlaneInclined plane made of a ramp used to lift an object

MA = length of ramp height of ramp

◦Gradual slant = greater MA, but greater distance

◦Steeper slant = less MA, but shorter distance

ScrewScrewScrew inclined plane wrapped around a nail

MA depends on distance btw threads◦Smaller distance = more MA

Wedge Wedge Wedge 2 inclined planes placed back to back; inclined plane that moves when used

Thick at one end, thinner at the other◦Thinner, more gradual wedge = greater MA

Wheel & AxleWheel & AxleWheel & axle wheel attached to a shaft

Increases the force you apply to the wheel

MA depends on the size of the wheel & thickness of axle